The new Azure AD B2C only supports OAuth2 and SAML2.0 - and NOT WS-Federation.
As far as I understand Dynamics 365 NAV and BC only supports the aged WS-Federation.
This off cause means that you cannot use Azure AD B2C with NAV/BC unless you put a 3rd party "translator" between the protocols in between.

Please add the more modern OAuth2 Single-Sign-On protocol to the BC (and NAV if possible) windows- and webclients.
Category: General
Needs Votes
Ideas Administrator

Thank you for this suggestion! Currently this is not on our roadmap. We are tracking this idea and if it gathers more votes and comments we will consider it in the future.

Best regards,
Business Central Team